Summary of Work: The Comparative Pathobiology Group has focused its research on defining the pathogenesis/carcinogenesis of disorders affecting the reproductive tract of humans and rodents, and assessing the role of environmental and endogenous factors in the induction of these disorders. Our group has used archival mouse and human tissues to determine the presence of growth factors in uterine leiomyomas ("fibroids") and leiomyosarcomas in mice and women. Data from our studies show that TGF-alpha (mature form) is expressed exclusively in malignant uterine smooth muscle cell tumors (leiomyosarcomas) of mice. However, in benign uterine smooth muscle cell tumors (leiomyomas) of mice and women this growth factor is not present. In mice, we have also found a positive correlation between TGF-alpha staining and immunoexpression of epidermal growth factor receptor, and increased cell proliferation as measured by the expression of proliferating cell nuclear antigen (PCNA) in the malignant uterine leiomyosarcomas. In women, we have found that IGF-I is overexpressed in unterine leiomyomas compared to normal myometrium during the proliferative phase of the menstrual cycle, and it appears that the IGF-I receptor signaling pathway is important in uterine leiomyoma growth. We have conducted studies to assess the role of Bcl-2 and Bax in modulating cell survival and death in human uterine leiomyomas. Our results show that both positive and negative regulatory proteins of programmed cell death (apoptosis) are present in human uterine leiomyomas, and that altered apoptosis does not appear to play a significant role in the development of these tumors through prolonged cell survival. We have successfully immortalized human uterine leiomyoma and normal smooth muscle cell lines by the insertion of the human telomerase gene. In vitro model systems for studying uterine leiomyomas are limited in that human derived leiomyoma cells grow poorly in culture and begin to senesce early. We have overcome this obstacle with the creation of an hTERT uterine leiomyoma cell line. These immortalized cell lines will allow us to assess uterine leiomyoma tumorigenesis in a prospective manner.